/Engine/Plugins/Runtime/MeshModelingToolset/Source/MeshModelingTools/Public/EditMeshPolygonsTool.h
Flip the selected (non-border, non-seam) edges, replacing them with new edges in the crossing direction
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(CallInEditor, Category=EdgeEdits, Meta=(DisplayName="Flip", DisplayPriority=1)) void Flip()